1. Field of the Invention
The present invention relates to a method and an apparatus for molding a cushion member from a fiber mixture which is a mixture of synthetic matrix fibers and binder fibers dispersed therein having a melting point lower than that of the matrix fiber (hereinafter referred to as "fiber mixture"), wherein the fiber mixture is filled in a mold cavity and heated therein. More specifically, the present invention relates to a method for molding a cushion member from a fiber mixture comprising the steps of filling the fiber mixture in a mold cavity formed by an air-permeable mold by a transportation air stream and finally passing a molding air stream for heating and/or cooling through the filled fiber mixture and an apparatus therefor.
2. Description of the Related Art
In general, a low cost urethane foam has widely been used for forming seat cushion members for automobiles or airplanes having a complicated configuration. However, the urethane foam has drawbacks in that a toxic gas is generated during combustion and a recycling is difficult, whereby substitute therefor has long been eagerly demanded.
To solve the above-mentioned problems, attention has recently been paid to a cushion member using the above-mentioned fiber mixture as a substitute for urethane foam. This cushion member has been formed by filling a fiber mixture into a mold cavity and heating the same to melt binder fibers contained in the fiber mixture to bond individual fibers composing the fiber mixture with each other.
Also, a method for producing a cushion member from a fiber mixture is proposed, for example, in Japanese Unexamined Patent Publication Nos. 2-95838 and 7-324266, wherein the fiber mixture is filled in a mold constructed from an air-permeable material while accompanied by a transportation air stream and hot air and cold air are made to flow through the fiber mixture filled in the mold cavity to mold the cushion member. This method has an advantage in that it is possible to quickly and uniformly heat-treat the cushion member because hot air and cold air are made to flow through the fiber mixture.
However, according to the above molding method, there is a problem in that a high quality cushion member is not obtainable if the cushion member has a complicated configuration as shown in FIG. 1 which is, for example, a backrest of a car seat, having a pouched structure F in the upper portion and an upright wall D on the respective side. This is because, a condition required for the transportation air stream in a process for filling the fiber mixture in the mold cavity while accompanied by the transportation air stream is different from that required for a molding air stream in a process for passing hot air and/or cold air through the fiber mixture (in this respect, "hot air and/or cold air" and "molding air stream" have the same meaning in the present invention). Details thereof will be described below.
In the process for filling the fiber mixture in the mold cavity, it is required that no void lacking the fiber mixture is generated within the mold cavity and the fiber mixture is filled at a predetermined bulk density. Accordingly, it is necessary to adapt the mold so that the transportation air stream for the fiber mixture more easily enters a portion of the mold cavity in which a void is liable to be generated. For this purpose, the air-permeability of the portion of the mold cavity in which a void is liable to be generated must be higher than in the other portion thereof.
Contrarily, in the heat-treatment process for passing the molding air stream through the fiber mixture filled in the mold cavity, it is required to uniformly pass the molding air stream through the mold filled with the fiber mixture so that no molding unevenness occurs in the resultant cushion member.
As is apparent from the above description, the behaviour of the air stream within the mold cavity is quite different between the filling process wherein the fiber mixture is gradually filled in the mold cavity and the heat-treatment process wherein the fiber mixture has already been filled in the mold cavity.
Further, usually, a shape of the mold cavity in the filling process is different from that in the heat-treatment process unless the molding condition is particularly unique. This is because that since the bulk density of the fiber mixture is low when the same is being filled, it is necessary to displace the mold in the compressive direction to compress tie fiber mixture to obtain a predetermined bulk density, which naturally results in the difference in the configuration of the molding cavity between the filling process and the heat-treatment process.
As stated above, the required behaviour of the air stream within the mold cavity is largely different between the filling process and the heat-treatment process in the configuration of the mold cavity, the flow resistance of the air stream through the fiber mixture, the flow path of the air stream or others. That is, the behaviour of the transportation air stream required for transporting the fiber mixture and that of the molding air stream required for converting the fiber mixture to the cushion member have different characteristics from each other. Thus, it is very difficult to obtain a high quality cushion member while avoiding a filling irregularity and/or the heat-treatment unevenness generated by the conventional molding method wherein the air-permeability of the mold is invariable between the filling process and the heat-treatment process in spite of such a large difference in the required characteristic between the both.
Such a fact causes a serious problem in a mass-production of the cushion member because a long time, for example, 30 minutes is necessary for slowly increasing and lowering the temperature of the fiber mixture to avoid the unevenness in the heat-treatment, which results in an excessively long molding time to slow mass-production and increase the molding cost.
To solve the above problem, there is a proposal in that a large amount of molding air stream is made to pass through the fiber mixture to improve the heat-transmission efficiency from the molding air stream to the fiber mixture. This method, however, requires a large flow rate of molding air stream which accompanies an increased air pressure. Accordingly, the fiber mixture which has been heated to lose its elasticity to some extent is liable to deform due to an influence of the large air pressure, whereby a thickness of the resultant product becomes thinner than the required thickness to deteriorate a quality of the cushion member.
To avoid this problem, it is also conceivable to accelerate the flow rate of hot air until the temperature of the binder fiber reaches a softening point and then decelerate the flow after the softening. During the cooling, cold air of a low flow rate is used while the fiber mixture is in a molten or softened state wherein the deformation thereof is liable to occur, which is then accelerated at the instant when deformation hardly occurs. Although this method is effective to some extent for shortening the processing time, it is impossible to largely reduce the heat-treatment time required for the heating/cooling process. Accordingly, it is extremely difficult to shorten the molding time of the cushion member, for example, to 5 minutes or less and it is impossible to reduce the molding cost by the mass-production while maintaining a high quality.
Also, according to a mold for molding a cushion member having a complicated configuration, such as a seat back as shown in FIG. 1 described above, the mold cavity to be filled with the fiber mixture also must have a correspondingly complicated configuration. Therefore, when the fiber mixture is filled in the mold cavity while accompanied by the transportation air stream, the behaviour of the transportation air stream within the mold cavity is difficult to control. Thus, it is extremely difficult to fill the fiber mixture in the mold cavity while stopping voids from being generated. Due to such a reason, it is very difficult to control the fiber mixture to be filled in the mold cavity in a desirable state.